The Isle of Thanet is an area of northeast Kent, in England, that used to be separated from the mainland by the Wantsum channel. The first bridge over the channel was built at Sarre in 1485. However, the channel silted up around the 15th century, and now the so-called isle is only partially separated from the mainland by the minor rivers Wantsum and Stour. Thanet contains the seaside towns of Margate, Ramsgate and Broadstairs, along with many other towns and villages.

Because of its proximity to France and therefore to mainland Europe, Thanet received the first of the Roman invaders in 55 BC. It was in Thanet that Vortigern formed an uneasy alliance with Hengest and Horsa, by tradition chieftains of the Jutes, who led the Anglo-Saxon invasion in AD 449. By the end of the fifth century, Thanet had become a Jutish kingdom.